The present application claims priority under 35 U.S.C. xc2xa7119 of German Patent Application No. 199 40 664.2, filed on Aug. 27, 1999, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The invention relates to a process for presetting a calender for a material web such as paper, cardboard, and the like. The calender has a roll stack comprising a lower roll designed as a sag compensation roll. This lower roll is rotationally secured via a carrier which can be lifted in the direction of the stack by utilizing external support devices which grip its ends. The lower roll also has a jacket which is supported on the carrier by internal support devices and the roll can be adjusted along its entire length in the direction of the stack. The calender also includes at least one middle roll which can be adjusted in the direction of the stack. Moreover, an upper roll, designed as a sag compensation roll is also utilized. The upper roll has a carrier which is held stationary at its ends and utilizes a jacket supported on the carrier by internal support devices. This upper roll is also seated on the carrier at its ends. The invention also relates to a calender for implementing this process.
2. Discussion of Background Information
Conventional calenders must be calibrated or preset before they can be loaded for a specific purpose. The aim of calibration is to produce a xe2x80x9cstraightxe2x80x9d nip between the rolls in each case, i.e., for the rolls to lie against each other so as to have the same pressure across the entire calender width, i.e., in order to create a uniform line load in the nip.
One conventional procedure requires calculating a load from the following determinations; internal pressure in the upper roll, the upper roll jacket weight, the middle roll weight, the lower roll jacket weight, and any friction values in the calender, and that the pressures to be applied to the external and internal support devices. The accuracy of the settings were then checked by testing a nip impression using NCR paper. Such a procedure is laborious and time-consuming because even slight deviations between the actual quantities and the calculated quantities lead to deviations in the line load. Moreover, when corrections are made on the basis of nip impression tests, one is never quite certain whether the pressures should be changed overall or whether a mere zone correction should be undertaken. Further, the procedure also has an element of danger because the NCR paper must typically be pushed into the nip by hand.
The present invention provides for the presetting or calibration of the calender. Accordingly, the present invention provides a process for presetting a calender including a stack comprising a lower roll designed as a sag compensation roll. The lower roll is rotationally secured via a carrier which can be lifted in the direction of the stack by external support devices gripping its ends. A roll jacket is supported on the carrier by internal support devices wherein the roll can be adjusted along its entire length in the direction of the stack. The calender also has at least one middle roll which can be adjusted in the direction of the stack and an upper roll designed as a sag compensation roll. The upper roll has a carrier which is held stationary at its ends and whose jacket is supported on the carrier by internal support devices. The upper roll is also seated on the carrier at its ends. Moreover, pressure can be applied to the internal support devices of the lower roll such that the jacket of the lower roll forms approximately a cylinder with a horizontal axis. Accordingly, in closing the nips, the external support devices of the lower roll or its internal support devices are loaded with an increasing pressure. The process also provides that pressures acting in the external and internal support devices at the instant of the complete closing of the uppermost nip are recorded.
Accordingly, if a calender is utilized whose upper roll is a sag compensation roll without a jacket lift and whose lower roll is a sag compensation roll with a jacket lift, wherein the carriers of the upper roll are held stationary and the height of the carriers of the lower roll are made adjustable by external support devices, the presetting can be performed in a very simple manner. When the jacket of the lower roll corresponds to a cylinder having a horizontal axis, as a result of its loading, and maintains this shape while the nip is being closed due to pressure tracking, corresponding cylindrical shape is formed by a jacket of the upper roll at the instant of the complete closing of the uppermost nip. As a result, straight nips can be obtained in the entire roll stack. Moreover, the pressures acting at this instant can correspond to the basic setting and, building on this, the operating pressure values can be set.
In addition, the uppermost nip can be first closed in the center and thereafter closed progressively towards its sides. According to this design, it is only necessary to observe the closing conditions of the nip at one or both ends and this enables a very precise setting.
According to this process, it is possible that when the calender is put into operation or when the loads are changed (e.g., when a roll is changed), the upper and lower roll pressures of the calender can be calibrated by a single closing.
By tracking the pressure, e.g., the pressure applied to the one support devices of the lower roll is followed to the pressure applied to the other support devices, the provides that the carriers and jacket of the lower roll maintain their correlation to one another.
Moreover, the closing of the uppermost nip can be effected not only by loading the external or internal support devices of the lower roll with an increasing pressure, but also by decreasing the equal pressures applied to the internal support devices of the upper roll, e.g., the pressure applied to the internal support devices of the upper roll is decreased to close the uppermost nip.
However, the application of equal pressure can yield the best results, e.g., wherein approximately equal pressure is applied respectively to the correlated internal and external support devices.
The calibrating procedure can also be carried out automatically, e.g., wherein the pressures are automatically changed until a measuring signal detecting the instant of the complete closing of the uppermost nip occurs.
Optical detection of the nip closing may also be particularly favorable, e.g., such that the instant of the complete closing of the uppermost nip is detected optically.
Additional measures may be advisable for tracking the lower roll, e.g., such as those relating to the pressures applied to the internal support devices of the lower roll can be changed so that the distance between the jacket ends and the carrier remains constant. Moreover, the projecting weights of the middle rolls can also be compensated for in the usual manner.
The calender for implementing the process of the invention may include a roll stack including a lower roll designed as a sag compensation roll, whose rotationally secured carrier can be lifted by external support devices gripping its ends. The lower roll may have a jacket which is supported on the carrier in the direction of the stack by internal support devices such that the lower roll can be adjusted along its entire length in the direction of the stack. The calender can include at least one middle roll which can be adjusted in the direction of the stack and an upper roll designed as a sag compensation roll. The upper roll can have a carrier and be held stationary at its ends and may include a jacket supported on the carrier by internal support devices. The jacket can be seated on the carrier at its ends. Such a calender is particularly suited for carrying out the process described above. Moreover, the calender can include, in the area of at least the one end of the uppermost nip, a measuring device which delivers a closing signal when this nip end closes.
The measuring device may be situated at precisely the point at which the uppermost nip finally closes, so that it is possible to determine the instant of closing very precisely. An optical measuring device may also be provided since such a device has proven to be particularly good in this connection. The measuring device can may also particularly utilize a light barrier, e.g., such as one which is interrupted when the nip end closes. The recording device may also be included for the purpose of documenting the base setting automatically, e.g., such as one which can record the pressures applied to the external and internal support devices that are in effect when the closing signal (S) occurs. Further, the calender can include a favorable arrangement for the tracking of the lower roll, e.g., a control device can be provided for the pressures to be applied to the internal or external support devices of the lower roll so as to keep the distance between the jacket ends and the carrier constant.
According to one aspect of the invention, there is provided a process for presetting a calender for a material web, the calender including a roll stack having at least a first nip and a second nip arranged to define a stack plane and comprising a sag compensation lower roll having a rotationally secured carrier which can be moved along the stack plane by external support devices arranged at both ends of the lower roll, the lower roll having a jacket which is supported on the carrier by internal support devices wherein the jacket can be adjusted along its entire length in the direction of the stack, the calender further comprising at least one middle roll which can be adjusted in the stack plane and a sag compensation upper roll having a carrier which is held stationary at its ends and a jacket which supported on the carrier by internal support devices, the jacket being mounted to the carrier at its ends, the process comprising applying pressure to the internal support devices of the lower roll such that the jacket of the lower roll approximately forms a cylinder having a horizontal axis, applying pressure to close each of the first and second nips, the pressure being applied to one of the external support devices of the lower roll and the internal support devices of the lower roll, and recording the pressures on at least one of the internal support devices of the upper roll, the internal support devices of the lower roll, and the external support devices of the lower roll at an instant of a complete closing of the first nip. The material web may be one of a paper web and a cardboard web and wherein the stack plane is a vertical stack plane with the first nip being arranged above the second nip.
The process may further comprise recording the pressures in each of the internal support devices of the upper roll, the internal support devices of the lower roll, and the external support devices of the lower roll at the instant of the complete closing of the first nip. The pressure applied to the support devices of the lower roll may be followed to the pressure applied to the other support devices. The process may include applying pressure to the internal support devices of the lower roll and thereafter applying pressure to at least one of the internal support devices of the upper roll and the external support devices of the lower roll. The process may further comprise decreasing the pressure applied to the internal support devices of the upper roll in order to close the first nip. The process may further comprise applying approximately equal pressure to each of the internal support devices of the upper roll, the internal support devices of the lower roll, and the external support devices of the lower roll. The approximately equal pressures may be correlated between each of the internal and external support devices. The process may further comprise detecting a measuring signal the instant the first nip is closed. The process may further comprise changing at least one pressure of the external and internal support devices based upon the detecting. The changing may comprise automatically changing the pressure when a measuring signal is detected. The process may further comprise detecting the closing of the first nip using an optical device. The detecting may comprise optically detecting at the instant of a complete closing of the first nip. The process may further comprise changing the pressure applied to the internal support devices of the lower roll in order to produce a constant distance between jacket ends of the lower roll and the carrier of the lower roll. The process may further comprise compensating for a projecting weight of the at least one middle roll.
The invention also provides for a calender for a material web comprising a roll stack defining a stack plane and comprising at least a first and a second nip formed by at least upper and lower sag compensation lower rolls with at least one middle roll disposed between the upper and lower rolls, the lower roll being rotationally secured on a carrier having ends, the carrier being moveable along die stack plane by external support devices arranged at the ends, the lower roll including a jacket which is supported on the carrier by internal support devices which can be adjusted along substantially an entire length of the lower roll, the at least one middle roll being adjustable along the stack plane, the upper roll including a carrier having ends which are held stationary and including a jacket supported on the carrier by internal support devices, the jacket having ends which are mounted on the carrier, and at least one measuring device arranged adjacent an area of at least one end of the first nip, wherein the measuring device produces a closing signal S when the first nip closes.
The material web may be one of a paper web and a cardboard web and wherein the stack plane is a vertical stack plane with the first nip being arranged above the second nip. The at least one measuring device may comprise an optical measuring device. The optical measuring device may include a light barrier which is interruptible when an end of the first nip closes. Each of the external and internal support devices may be operable via hydraulic pressure. The hydraulic pressure in at least one of the external and internal support devices may be changed as a result of the closing signal S. The calender may further comprise a recording device for recording pressures in one of the external and internal support devices. The calender may further comprise a control device for regulating pressures to the internal or external support devices. The control device may be adapted to maintain a constant distance between the jacket ends and the carrier of the lower roll.
The invention also provides for a calender for a material web comprising a roll stack defining a stack plane and comprising at least a first and a second nip formed by at least first and second sag compensation rolls with at least one middle roll disposed between the first and second rolls, the first roll comprising a stationary carrier and a jacket supported on the carrier by internal support devices, the jacket being rotatably mounted on the stationary carrier, the at least one middle roll being adjustably moveable along the stack lane, the second roll comprising an adjustably moveable carrier and a jacket supported on the carrier by internal support devices, the carrier being moveable along the stack plane by external support devices, and at least one measuring device arranged to detect the closing of the first nip, wherein the measuring device produces a closing signal S when the first nip closes.
The invention also relates to a process of presetting a calender for a material web using a calender including a roll stack defining a stack plane and comprising at least a first and a second nip formed by at least first and second sag compensation rolls with at least one middle roll disposed between the first and second rolls, the first roll comprising a stationary carrier and a jacket supported on the carrier by internal support devices, the jacket being rotatably mounted on the stationary carrier, the at least one middle roll being adjustably moveable along the stack plane, the second roll comprising an adjustably moveable carrier and a jacket supported on the carrier by internal support devices, the carrier being moveable along the stack plane by external support devices, and at least one measuring device arranged to detect the closing of the first nip, wherein the measuring device produces a closing signal S when the first nip closes, the process comprising applying pressure to the internal support devices of the second roll such that the jacket of the second roll assumes approximately a cylindrical shape, applying at least one of pressure to the external support devices and additional pressure to the internal support devices of the second roll in order to cause the second roll to contact the at least one middle roll, applying at least one of additional pressure to one of the external support devices and the internal support devices of the second roll, wherein the additional pressure causes movement of the at least one middle roll against the first roll such that the center of the middle roll contacts the center of the first roll before the ends of the middle roll contact the ends of the first roll, detecting, with the at least one measuring device, contact between at least one end of the at least one middle roll with at least one end of the first roll using the at least one measuring device, producing the closing signal S when the first nip closes, and recording the pressure in one of the of the internal support devices of the first roll, the internal support devices of the second roll, and the external support devices of the second roll at the instant of the complete closing of the first nip.
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawings.